Model Output Discussion 18th Nov.2013-12z onwards.

[Frosty.]

Impressive GEFS 00z mean this morning, the best of the season so far and it's not even winter yet. a cold unsettled blast is growing in confidence and december as a whole could be on the cold side and unsettled...it's going to be a long winter with lots more of this and hopefully some Beasterlies too.

[SMU]

Yes AVFC we have- however the ECM only run the amplification for 2 days - then settled back down - so yes, we do have to temper all enthusiasm, although last time was more difficult route & more difficult to predict as the epic charts were based on a volatile track of a tropical system, at least here we have a more 'normal' type pattern.

 

 

Catacol- its not all about the stratosphere- Firstly what you are seeing are models - the same models that we look at day in day out that make errors, Secondly The correlation of Cold stratosphere to warm OK is not a linear 1:1 relashonship- its probably something like 0.7 -

rather similar to the relationship the UK has with the AO- ie most of the time an -AO index will mean the uk becomes cold- but not always....

 

Which means in an overall cold stratospheric profile you can still develop small waves & small pressure anomalies over 60N without interrupting the overall mean flow of the jet-

 

indeed someone posted the CFS run from yesterday post boxing day earlier-  a CLASSIC example of a 15 day period for the UK at or near zero with next to no SIGNIFICANT blocking, apart from the first days ridge the blocking doesn't exceed 552 DAM over Greenland - so certainly nothing high about the anomaly- but enough to move the jet south & circulate very cold air around the southern flanks....

 

Also look at the December 1995 CET- 2.3c ~ 3 degrees below the norm-

 

very cold stratosphere-

 

http://www.cpc.ncep.noaa.gov/products/stratosphere/temperature/archive/70mb9065_1995.gif

 

but the AO wasnt negative & the mild blocking lived around Greenland-

 

notably the profiles of the stratosphere are MORE like 95 than 81 so maybe 95 is the form horse index wise....

Look at the height profiles teleconnected from the Aleutian High to the Greenland high.- but no polar blocking.

 

S

Edited November 27, 2013 by Steve Murr

[Frosty.]

The Ecm 00z ensemble mean is looking better and better, it's probably going to become even better as time goes on with the high to the southwest shoved even further away from the uk. A lot of us have been posting charts and banging on about cold blasts and had scorn poured over us, but here they are, creeping closer and closer.

[Catacol]

Yes AVFC we have- however the ECM only run the amplification for 2 days - then settled back down - so yes, we do have to temper all enthusiasm, although last time was more difficult route & more difficult to predict as the epic charts were based on a volatile track of a tropical system, at least here we have a more 'normal' type pattern.

 

 

Catacol- its not all about the stratosphere- Firstly what you are seeing are models - the same models that we look at day in day out that make errors, Secondly The correlation of Cold stratosphere to warm OK is not a linear 1:1 relashonship- its probably something like 0.7 -

rather similar to the relationship the UK has with the AO- ie most of the time an -AO index will mean the uk becomes cold- but not always....

 

Which means in an overall cold stratospheric profile you can still develop small waves & small pressure anomalies over 60N without interrupting the overall mean flow of the jet-

 

indeed someone posted the CFS run from yesterday post boxing day earlier-  a CLASSIC example of a 15 day period for the UK at or near zero with next to no SIGNIFICANT blocking, apart from the first days ridge the blocking doesn't exceed 552 DAM over Greenland - so certainly nothing high about the anomaly- but enough to move the jet south & circulate very cold air around the southern flanks....

 

Also look at the December 1995 CET- 2.3c ~ 3 degrees below the norm-

 

very cold stratosphere-

 

http://www.cpc.ncep.noaa.gov/products/stratosphere/temperature/archive/70mb9065_1995.gif

 

but the AO went negative & the mild blocking lived around Greenland-

dec1995.png

 

notably the profiles of the stratosphere are MORE like 95 than 81 so maybe 95 is the form horse index wise....

Look at the height profiles teleconnected from the Aleutian High to the Greenland high.- but no polar blocking.

 

S

 

Agreed - Dec 95 is a much better profile for comparison. I got my best ever south of England snow event in Feb 96 so you have my full interest and support if anything like that is in the offing! :-)

 

I think my point, slightly gloomy though it is, is that sustained high lat blocking is going to be hard to achieve in December. I agree that the strat / trop correlation is not and cannot be 1:1 - the position of the vortex has error bars outside of model accuracy and if wave amplification synchronises correctly with vortex movement or wobble then we can cash in... but it is hard to achieve.

 

If I thought the chances of real cold were 0 I wouldnt keep pulling up the charts/models/teleconnections and looking for something special. We all believe and hope it can come - but on the balance of probability at the moment it is going to be tough to see anything other than a transient northerly.

 

I would be delighted to be proved wrong...

Edited November 27, 2013 by Catacol_Highlander

[Joe Levy]

Interestingly, as Frosty has just inferred, some of the key building blocks, if you like, to us receiving cold weather over the next couple of weeks are now falling into a much closer time frame and so there can no longer be the same argument that this is all in FI. However, stay alert for anything that might scupper our chances, such as shortwaves. Equally, keep an eye out for anything that might prolong the cold. All options are still possible but currently, the way things stand, cold weather is becoming increasingly likely.

[Bristawl Si]

Looks like a fairly 'typical' spell of UK December weather coming up for the next couple of weeks.

By that i mean, colder incursions from a NW direction, with the obvious candidates seeing more of it (further North). Gradually as December goes on we may see more 'snaps' with milder in between.

This is how i remember December's weather to be - (forget 2009 and 2010 they were exceptions in my lifetime, plus 1981 of course!).

'Real' winter normally starts after Crimbo down here - if it does at all.

[draztik]

The ext ecm ensembles show milder uppers by Tuesday 10th, and these build as we move forward after this; due to heights building over the UK and moving NE.

heres day 13 &15 showing temp anomaly

day 14 heights anomaly

this has been the indication from the ens the last few runs

[Frosty.]

Looks like a fairly 'typical' spell of UK December weather coming up for the next couple of weeks.By that i mean, colder incursions from a NW direction, with the obvious candidates seeing more of it (further North). Gradually as December goes on we may see more 'snaps' with milder in between.This is how i remember December's weather to be - (forget 2009 and 2010 they were exceptions in my lifetime, plus 1981 of course!).'Real' winter normally starts after Crimbo down here - if it does at all.

I always thought typical uk December weather was sw'ly mush or euro high's. Things are looking wintry to me.

[Joe Levy]

This lovely chart from GFS but in FI of course!

[Methuselah]

I do hope it's more than the usual pre-Xmas rampede? It looks colder & more unsettled, yes; but comparisons to '81 and '95 may be a tad premature... 

[swfc]

would seem the 6z drops the low on the oz around the 240 hr mark and looks atm more akin to ecm?for now anyway

[gottolovethisweather]

I do hope it's more than the usual pre-Xmas rampede? It looks colder & more unsettled, yes; but comparisons to '81 and '95 may be a tad premature... 

 

Just something to aim at.  We still need to listen to what the pros have to say and also keep our coldie's feet firmly on the ground. However, a change is a coming and initially it sure won't be coming up on a SW'rly moisture laden airmass.

[That ECM]

http://images.meteociel.fr/im/4214/gfs-2-216_gag0.png

What could possibly go wrong?!

[Yarmy]

I do hope it's more than the usual pre-Xmas rampede? It looks colder & more unsettled, yes; but comparisons to '81 and '95 may be a tad premature... 

 

It's why I don't like analogues much, although I respect the insight (and memory!) of those that post about them.

 

After all,  all of the models are near identical analogues of each other at the start of their respective runs, yet they all look very different at T240 (and the actual weather different to each of them). 

[beng]

 

We need something far more aggressive to be thrown at the vortex if we are truly to unlock the cold. If we get ridging into the arctic without any warming episode occurring then a disconnect would be more obvious... but to be honest since following the Strat thread carefully I cant remember seeing such a disconnect at any stage. December 81 isnt a great example to use because December strat temperatures bottomed out at -70 (we are close to -80 now) and there was a Canadian Warming that month that will have helped the development of a blocking pattern downstream. So the strat and the trop on that basis were very much connected.

 

Following that train of thought what we really need to see therefore is a Canadian Warming and we need to see it soon otherwise nothing remarkable this side of Xmas remains likely.

 

I think it's just a question of patience.  With the QBO phase and the fact we're in solar max (although the sun's gone quiet again for the moment) - there's a really good chance of a decent warming later on - but probably not for another month.  I think it's quite ominous though that even with the rampant vortex, we're still seeing a below average November CET and the Alaskan ridging, and possible cold shots from the North. As soon as we see some warming later on, I suspect the vortex's going to get crushed (assuming the broad pattern is similar). Cold lovers need to hope for a late Dec warming, rather than late Jan warming though. 

[R.P. McMurphy]

I do hope it's more than the usual pre-Xmas rampede? It looks colder & more unsettled, yes; but comparisons to '81 and '95 may be a tad premature... 

 

You were saying!??!?!

[Gibby]

IMO despite some optimism this morning I can't see any excitement to be gained from the 10 day mean chart of ECM. High pressure to the SW means there is no way cold will last a day or two on that synopsis.

 

http://www.wetterzentrale.de/pics/Reem2401.gif

[Bristawl Si]

I always thought typical uk December weather was sw'ly mush or euro high's. Things are looking wintry to me.

i think i mentioned cold snaps with mild as well. ie a mixed bag. Bulk standard for Dec.

[Methuselah]

 

You were saying!??!?!

It wasn't me. It was an impostor! 

[Frosty.]

Well...the Gfs 06z op run would deliver rather more than standard uk December weather for sure, looks more like Dec 2010 to me, snow all over the uk, severe frosts and a bucket full of ice days followed by a frosty high to hard pack all that deep snow.

Edited November 27, 2013 by Frosty.

[R.P. McMurphy]

IMO despite some optimism this morning I can't see any excitement to be gained from the 10 day mean chart of ECM. High pressure to the SW means there is no way cold will last a day or two on that synopsis.

 

http://www.wetterzentrale.de/pics/Reem2401.gif

Morning Gibby,

 

It still remains cold, the HP isn't exactly a scorcher either, perhaps the far SW possibly touching double figures, while everyone else remains in single digits and cold frosty mornings. 850's -10C.

 

[weatherguy]

It's exciting to see the prospect of some good cold weather on the way (albeit tentative signs this far out), but I will echo what others are saying...

 

Barring exceptional circumstances, no cold spell is going to be anything special in terms of severity/longevity, not while the stratospheric vortex is in such good shape.  I wrote this about a week ago:

 

 

In my opinion, I can't see any sustained cold for at least the next 2 weeks.  At the same time, it certainly doesn't look zonal, with positive HP anomalies centred near to the UK.  As a result, natural wobbles in the PV will leave us in with a chance of receiving topplers, so wintry weather is possible.

 

And it seems to have been a reasonable forecast.

 

Let's just hope we can continue to eek out these cold snaps as we progress through December, until we start to see some more favourable teleconnective signals as we head into Jan/Feb.  And hey, no sign of anything (mild) zonal yet, so I'm sure us coldies can be thankful for that 

[summer blizzard]

IMO despite some optimism this morning I can't see any excitement to be gained from the 10 day mean chart of ECM. High pressure to the SW means there is no way cold will last a day or two on that synopsis.

 

http://www.wetterzentrale.de/pics/Reem2401.gif

 

Looking at the very weak low to the west i'd expect that high to be retrogressing and amplifying somewhat. Probably too close to the UK for widespread snow but still pretty chilly.

[carinthian]

Well...the Gfs 06z op run would deliver rather more than standard uk December weather for sure, looks more like Dec 2010 to me, snow all over the uk, severe frosts and a bucket full of ice days followed by a frosty high to hard pack all that deep snow.

 Frosty, I would say that is a cold wave moving from the Arctic , through Britain into  Europe if  those charts are to materialize ?

C

[snowmadchrisuk]

It looks possible to me that at some point we could get an Arctic high/ Azores High link up , that would put the wheels in motion for a more prolonged cold spell.